Implement SIP6

[braydonf]

Implements https://github.com/Storj/sips/blob/master/sip-0006.md

Combines these branches for development:

• Implement SIP6 core#704
• Implement SIP6 complex#71
• Implement SIP6 service-storage-models#117
• Implement SIP6 bridge#464
• [WIP] Implement SIP6 storjshare-daemon#230

Todo:

• Add publishContract to complex client
• Update lastContractSent on the contact when publish message sent (or equivalent)
• Update storage models to have updated fields for contact and necessary indexes
• Connect _selectFarmers and _publishContract to addShardToFrame
• Make sure that contract is sent to nodes/farmers with capacity available
• Determine value for PUBLISH_BENCH_THRESHOLD (now configurable)

Testing:

• Change config/storj-bridge/config.json value activateSIP6 to true and false and test uploading as described at https://github.com/Storj/integration#testing-file-transfers
• To test SIP6 further:
  • Comment lines for farmer.join in ./scripts/farmer.js in storjshare-daemon
  • Run ./script/stop_everything.sh
  • Clear the contacts collection from mongodb
  • And then ./scripts/start_everything and check that farmers join the bridges by looking at mongo
  • Test that uploads are working as expected